X-ray tube sighting device



- Dec. 14, 1948. T. R. HAWKS X-RAY TUBE SIGHTING DEVIC E Filed July 29, 1944 5 Shets-Sheet 1 Dec. 14, 1948. T. R. HAWKS 2,455,928

X-RAY TUBE SIGHTING DEVICE Filed July 29, 1,944 5 Sheets-Sheet 2 l f I I1 I J f 68 30 j 52 a ll v r 5O 44 1Q i i Q 24 7 B I I28 72 LJ Dec. 14, 1948. R HAWKS 2,455,928

I X-RAY TUBE SIGHTING DEV ICE- Filed July 29, 1944 Y s Sheets-Sheet s 1 1%6. IJQZ Dec. 14, 1948. HAWKS 2,455,928 I X-RAY TUBE SIGHTING DEVICE Filed July 29, 1944 5 SheetsSheet 4 Dec. 14,1948. T. R. HAWKS 2,455,928

X-RAY TUBE SIGHTING DEVICE 5 Sheets-Sheet 5 Filed July 29, 1944 Patented Dec. 14, 1948 -UNITED STATES PATENT OFFICE 2,455,92 X-RAY TUBE SIGHTING- DEVICE Thomas Richard Hawks,-Washington, D. C.

Application July 29, 1944, Serial No. 547,239 1 4 Claims. (01. 250-64) (Granted under the act of March 3, 1883, as

This invention relates to X-ray machines and more specifically to'means to facilitate. the alignment of the X-ray tube with the film holder and patient.

In one type of X-ray machine the X-ray tube is'supported above a table suitable to sustain a patient and for holding a photographic plate'or film in a position to photographicallyrecord that portion of the patient to be examined. The X-ray tube is customarily mounted forsub-stantially universal movement with respect to the table and heretofore has been brought into alignment with the patient and film holder by trial and errori While this method is fairly satisfactory for experienced operators and when the photograph is to be taken perpendicular to the table; when it is desirable to take 'a photograph at angles less than right angles with respect to the table it is difficultto align the X-ray tube, patient-and film holder. It is an object of the present invention to make the alignment of the X--raytube, patient and film holder (hereinafter to be referredto as the cassette) accurate, rapid, and simple for even an unskilledoperator;

--In one aspect in'vention resides in means associated with the X-ray tube for observing an image of the cassette, a ref erence mark associated with saidmeans and a sight, the first named means, reference mark and sight being so arranged with respect to each otherand the X-ray tube that when the operator sees a given pointon the image of the cassette and the sight superposed in the first named means at said reference mark, the axis of the projected rays from the X-ray tube will intersect the cassette at said point. More specifically the means for centering the X-ray tube with respect to a given point on the cassette comprises a mirror forreflecting an image of the cassette'for observation, a reference mark on the mirror in the form of hair lines crossing at right angles and a sight of the bead or reticule type soarranged with respect to the X-raytube that when the image of said given point on the cassette andth'e sight are observed in the mirrorto-be superposed at the center of the reference mark the X-ray tube will be in alignment with said given point on the cassette. In one instance the sight is in the form of a. transparent plate having crossed hairs formed on its surface the sight being located between the mirror and cassette so that the op-' erator sees images of both the sight, that'is the cross hairs, and the cassette in the mirror. How

ever, the sight may be of the bead type and may be located adjacent to the X-ray tube but not amended April 30, 1928; 370 0. G. 757) between the mirror and cassette. In this instance the operator sees the image of the cassette and the cross hairs on the mirror directly behind the bead sight.

As illustrated herein there are provided two means for aligning'the X-ray tube, one of which is mounted in a position to-be adjustable with the 'X-ray tube about the longitudinal axis of rotation of the X-ray tube and the other one of which is mounted in a position to be adjustable with the X-ray tube about the transverse axis of rotation of the X-ray tube. 'It is inconvenient to have to look first into one means and then into the other while aligning the X-ray tube because of the necessity of moving the head from one position to another.

Accordingly, novelty also resides in constructing one of said means so that it may be adjusted with respect to the X-ray tube for any given distance from the cassette to provide for alignment of the X-ray tube not only about the axis upon which it is mounted for rotation; but also for alignment of the X-ray tube about the axis at right angles thereto. This is accomplished herein by bringing the X-ray tube into alignment with the cassette at a given height by employing both means and then adjusting the angular position of the mirror and sight of one of said means so that at said given height the image of the cassette and sight will be observed to be superposed at the reference mark on the through which the X-ray are projected. Novelty also resides in a modified form of the invention which is adapted to be readily attached to the open end of the cone shaped shield. In this form the mirror and sight are supported at the end of the cone'shaped shield by a device which automatically centers the mirror with respect to the axis of projection of the X-rays. Still another form of the'invention which is especially suitable to be carried around and which in use is placed against the Wall of the cone shaped shield comprises a'spindle to' Which is attached a mirror and sight the arrangement being such that a given portion of the wall of the cone shaped shield maybe aligned with a given point on the cassette by adjustment ofthe X-ray tube until the imaged the given point on the cassette and the sight are superposed at the reference mark on the mirror. In some X-ray machines, the

shield is cylindrical in shape, hence means is provided for changing the position of the spindle with respect to the wall of such a shield.

The invention will now be described in detail with reference to the accompanying drawings in which:

Fig. 1 illustrates apreferred form of my invention mounted on the head of a conventional X-ray machine;

Fig. 2 is a plan view of the head of the X-ray machine illustrating in particular the relative positions of my sighting means; i

Fig. 3 is a front view taken on line 3--3 of Fig. 1;

Fig. 3a is a fragmentary perspective view showing the projection of the cone of X-rays on the table;

Fig. 4 is a perspective view of the form of the sighting device used at the end of the X-ray tube for adjustment of the tube transversely of the table;

Fig. 5 is an end view of the sighting device shown in perspective in Fig. 4;

Fig. 6 is a perspective view of the form of the sighting device used midway between the ends of the X-ray tube for adjustment of the X-ray tube longitudinally of the table;

Fig. 7 is an end view of the sight shown in Fig. 6;

Fig. 8 is asection on the line :8--8 of Fig. '7;

Fig. 9 is a view on the line 99 of Fig. '7;

Fig. 10 is a side view of Fig. 9.; v

Fig. 11 is a side View of a form of sight which may be employed in lieu of the sighting means used for longitudinal alignment of the X-ray tube;

Fig. 12 is a front view of the formshown in Fig. 11;

Fig. 1-3 is a modified view of my invention which is detachably mounted on the open end of the shield of any X-ray head and is provided to take care ofboth transverse and longitudinal adjustment of the X-ray tube;

Fig. 14 is a plan view of the top side of the device shown in Fig. 13;

. Fig. 15 is aplan view of the bottom side of the device shown in Fig.13;

Fig. 16 is a section on the line l6-|6 of Fig. 15; Fig. 17 is a front view of another modified form of the invention particularly suitable to be carried around; illustrating its use with a cone shaped shield, and applied to the wall of the cone near the observer;

I Fig. 18 is a side view of the device of Fig. 17 partially in section;

.Fig. 19 is a view of the device as used when applied to the wall of the cone at one side thereof in respect to the observer;

Fig. 20 is a View of the device partially in section illustrating its use with a cylindrical shaped shield; and

Fig. 21 is a bottom view of the device.

Referring to Fig. l the invention is shown as applied to the head N3 of a conventional X-ray machine, the head being mounted for substantially universal adjustment above a table indicated at [2 upon which a patient 14 may be placed for observation and for photographing. The cassette'l-B, that is the device for holding the film, may be placedbeneath the table .12 or. above the talblebenea't'h the patient and the invention relates to means 18 and 26 mounted on the head for aligning the head and hence the anode of the X-ray tube with a given point generally the center of the cassette so as to insure obtaining a 4 photograph of the patient which is centrally located with respect to the film.

The head I0 which is also of conventional design comprises a cylindrical housing 22, Figs. 2 and 3, which protects the X-ray tube from damage having a pair of laterally extending conduits 24 through which pass conductors 26 for energizing the X-ray tube. An opening 21 is provided in the lower side of the housing 22 below the anode of the X-ray tube and surrounding this opening is a cylindrical neck portion 28, the lower end of which is provided with a radially extending flange 30. A block 32 provided with a corresponding radially extending flange 34 is fastened to the flange 30 by means of screws. The block 32 has a central aperture 36 which is concentric with the cylindrical neck 28 and is provided on its lower surface with a transverse way 38 having grooves in its opposite walls for slidably receiving a plate 48 having tongues on its opposite edges which cooperate with the aforesaid grooves. Theplate isalso centrally apertured and has fixed thereto over the aperture a cone shape'd shield 42.

By positioning the plate 40 properly in the block 82 the cone shaped shield 42 may be lined up with the aperture in the block 32 and hence aligned axially with the anode oi the X-ray tube so that the X-rays projected therefrom pass centrally through the shield 42. The shield 42 is formed of lead and acts as a shield to prevent the scattering of the X-rays which would be dangerous to the operate rand the patient. While the shield is is illustrated in Fig. l, as cone shaped it may be cylindrical in shape as illustrated in Fig. 20. The head I0 is mounted for movement transversely of the table I2, between a pair of spaced sleeve like members 46 which in turn are slidably mounted on a pairof horizontal parallel spaced rods 44, Fig. '1, the latter being fixed at one end to a yoke 48. The outer ends of the rods 44 are braced by a pair of converging rods 50 which are attached at one end to the yoke 48 and are connected at their opposite ends to the rods 44 by means of a plate 52. The yoke 48 is pivotally attached .to a boss 56 formed on an upstanding column 58 the pivot 54 providing for adjustment of the headabout a horizontal axis. By tilting the X-ray tube about the pivot 54 the X-ray tube may be adjusted longitudinally of the table. To provide for tilting movement of the head transversely of the table the block 32 is journalled on the inner ends of a pair of oppositely disposed screws 60, Fig. 3, which are threaded through the spaced-members 46. An arm 62 is attached to the block 32. A spindle .64 is attached to the arm 62 and has a screw knob and pointer 66 secured to its outer end which provides convenient means for tilting-the head and for simultaneously indicating the degree of tilt.

The means for aligning the X -ray tube with respect tothe cassette and patient as shown in the various forms of my invention in general comprises a mirror 68 forrefiecting an image of the cassette It for observation, the mirror having formed thereon a reference mark 10 which may be a single scratch line or two scratch lines crossed at right angles and a sight 72 located between the mirror and the cassette or at a point adjacent to the mirror but not between it and the cassette, as illustrated in Figs. 11 and 13. The mirror, reference marks, and sight are so arranged with respect to the X-ray tube that when the center of an image of the cassette or some given point thereon as seen in the mirror are my invention, and to the sighting means I8 for.

positioning the X-ray tube, longitudinally of the cassette that is lengthwise of the table as seen in Fig. 3a, the device comprises as shown in Figs. 6

to 10, inclusive, a mirror 68 having a reference mark 10 which in this instance is a point formed on the surface of the mirror and a sight I2. The mirror 68, Figs. 6 and 7, is attached to a plate or bracket 82 which is hinged at 84 to a plate 86, the latter having fastened to its rear surface an angle bracket 88 which is adapted to be attached as shown in Fig. 1 to the flange 30 in such a position that the operator may see into the mirror without difiiculty. (Fig. 1.) The plate 82 is yieldably held by a spring 90 attached between hooks formed on the plates 82 and 88 against a cam 92 the latter being mounted on a spindle 94 journalled in an inturned ear 96, Fig. 6, the spindle 94 having a knurled knob 98 thereon which provides means for rotating the cam 92 and hence for adjusting the angular position of the plate 82 with respect to the plate 86. The sight I2 in this instance takes the form of a transparent plate I which may be of glass or plastichaving .formed thereon crossed scratch lines I02 and concentric circles I04. The plate I00 is inserted in a grooved block I08 and is fastened thereon by rivets the block I06 being arranged to be moved toward and away from the mirror 68. To this end the block I06 is provided with a rearwardly extending arm I08-which projects through a slot IIO formed in the plate 82. A pin II2, Fig. 8, is journalled in the rearwardly extended arm I08 with its opposite endsextending beyond the sides of the arm and is adapted to receive leaf springs II4, Fig. 10, which bear against the rear surface of the plate 82 and hence yieldably hold the block I06 against the plate 82 and yet permit adjustment of the block along the in a given position. As will be observed the bracket'l22 is fastened to the upper edge of the mirror. In Fig. 12 there is shown beside the usual reference mark I0 additional reference marks I26. The reference marks are designated 25, 30

o and 40 and so positioned that when the bead I I0 slot H0. The adjustment of mirror 68 angularly with respect to the plate 86 and of the sight I00 with respect to the mirror 68 permits the operator to set the device so that the X-ray tube will be aligned not only longitudinally of the table but also transversely of the table at any given height of the X-ray tube from the surface of the table.

The manner in which this is accomplished will be described hereinafter.

A somewhat simpler device for aligning the X-ray tube is indicated in Figs. 11 and 12. In this instance, a mirror 68 is employed as in the previous case the mirror being, however, attached directly to the flange 30. The mirror has the usual reference mark I0 but in place of the sight 12 used in the previous construction a wire H6 having a bead sight H8 is employed. In this case, the bead sight I I8 is not positioned between the mirror and the cassette. As will be seen by reference to Fig. 11, the sight is mounted adjacent to the mirror and between the operator and mirror. The bead sight II8 isadjustably fastened to the mirror by passing the upper end'of the wire II6 through the shank of a screw I20 the screw in turn being passed through a bracket I22 and secured in place by a nut I24. By turning the nut the wire may be jammed between the bracket and head of the screw so as to clamp it is lined up with a given reference mark the X-ray tube will be angularly positioned with relation to the cassette to insure correct alignment of the X-ray tube transversely of the cassette for the distanceit is away from the cassette as indicated by the'numeral opposite the reference line.

The means described above provide for longitudinal adjustment of the X-ray tube and may be adjusted to align the X-ray tube transversely of the tube so that the X-ray tube may be brought into proper alignment both transversely and longitudinally for a given height with a single device. The means 20 is provided for initially obtaining correct alignment of the X-ray tube transversely whereupon the means I8 may be set by adjustment of its mirror and sight to bring them into such relation that when the image of the cassette and the sight are seen to be superposed in the mirror at the center of the reference mark the X-ray tube will be aligned transversely of the cassette. Themeans 20' shown in Figs. 4 and 5 comprises a mirror 68 having a reference mark I0 thereon attached by Welding or soldering to the inner surface of a cylindrical housing I28 having abracket or collar I30 thereon by means of which it may be attached to one end of the housing22 as indicated in Figs. 2 and 3. The housing I28 is so positioned that the surface of the mirror is at an angle of 45 with the axis of theshield 42, Fig. 1. Beneath themirror and mounted onthe flange 30 is placed the sight I2, which in this instance, as shown particularly in Fig. 3, comprises 'a flat strip like member I32 placed on edge in a horizontal'position parallel to the referen-cemark 10. The position of the mirror 88, reference mark I0 and sight I2 are such that when the operator observes an image,v

of the cassette and the sight superposed in the mirror at the reference mark the axis of the shield 42 and'hence the anode of the X-ray tube will be in'transverse alignment with the center of the tube. Referring to Fig. 1, for example, if the operator I4 looks into the mirror 68 and sees the point I6 of the cassette and sight I2 in super-v posed position at the reference mark 10, he is in fact looking along a line of sight so positioned that "a given point on any object placed on the table will be aligned with respect to the X-ray tube and cassette, if the aforesaid given point on the object lies inthe line of sight. It is evident therefore thatthe operator may look into, the mirror'and align the patient so as to bring .a particular portion of the body into alignment with the X-ray tube and cassette for photographing by shifting or orienting the patient until the particular spot desired for photographing is brough into the aforesaid line of sight.

It may be desirable in certain instances to provide sighting means which is not necessarily permanently attached to the X-ray apparatus and hence there is provided as shown in Figs. 13 to 16, inclusive, a detachable holder I36 arranged to be mounted at the open end of the shield 42 for sup- QKK t i lQ azted-balhl 44.. rhe platess are I45 and. are yielde held-bathe e. .LbY-i. ably urged towarcleachetherby a pair of' springs srosmtbetw en the,-str.aps m5. Theplates 'nterconnected by links I48to an arm I50 wh el is pivotally attachedat :I to the bar I44. Eac ptatefiihifi provided near its outer edge with wn... 2 sneeedpim having necked ends I54 whic I56.

he openehdofthe shield-42. The aforesaid e is't t is suchthat when the holder 13s is placed against the loyver edge of the shield by Dl-$i g he plates I 38 apart Sufiiciently to allow engagementof the necked end portions I54 of the pins yvith theturnededge. I 56 and the plates are releasedtt e; holder; Will automatically center seliw; hgesp ctto .theexis of the shield. A d set ofe pins lfiii are. provided at the inner oh-the pl es; I38 to take care .of shields of g u ;.The fl'ml lOI III. is mounted ati thecenter of the {oar I l l at an angle of approxima ely iiig, 3v h;the plane of the mouth of the shield a-nd a sight I2;, is, mounted at one end of the bar H4 in such a .positionwith respect to the re ierence marlg Ill ,on the; mirror; that when the the cassette and sight 1-2 are seen super page?! II; the rnirrorat the reference mark the axis- (gt-the 51116316; will. be in ali nment with the center-of the cassette. I I

gIfh e iorm;of ;-the .invention just described is some hat bulky andcannotbe conveniently carried around andhence a pocket device-is shown hereinwhichgmay be'usedon anyexisting equipment T modification :of ,,theI invention is gs.;l7-to 21 inclusive; and comprises therusual-mirror 68;,reference mark III. and sight 12;.\ ;.Ihe mirrorfifl is :fastened to ablock 158 the block in turn being secured to a spindle I60 which adaptedto engage therolled over edge I I .the way position asshown inFig. 18.

'In-using the sighting means illustrated'in Figs. l-to .12, the operator places the cassette on'or' below the tabIe -IZ as'may be desired and then as shown in Fig. 18 may be held by the operator against theirs-her surface of the shield 42. The angle-at which -the mirror is positioned 'is such thatavhen the image of. a givenpoint onthe cassette preierably nearits perimeter and the sight e observed, to hesuperposed at .the reference markflilthatperipheral portion of theshield against-.Which the spindle I-6I!;is, held-will lie inlinewith thatgiven pointpnthe cassette; The

X- rayrtube may-be a-lignedwith the cassette with onlyone setting of-this device,;:h0wever, it is desirable to establish several points in orderv to in-' sure.al-ignment of. the *X-ray itubeowith the" cassette This-may be, done by the operator holdingthe device againstthe wall-of the wheat any point in its circumferencer as indicatediin Figs. 1'7 and l9. The ;upper edge of @the block I58, as indicated at i59 isatright angles: totheplongiw tudinalaxisofthespindle- I80 and hence theide vicemaytheheld in,- -the--corr ect position by bringing theupp er edge I59 into engagement with the rolled over edge of the shield 42;. The shield,

frequently referredto as the cone, is not always conical Itmay be -cylindrical as illustrated in Fig.2!) and to, make th'e' deviceladaptable to both forms o fi the, shield; a-. collar; I5 :isslidably mounted. on, .the spindle -Ipfl so -that the angle of the spindle -,I 6 w th respect to. the; surface ofthe shield may be varied. A series of annular notches I 1 0 :are formed in the-spindle for the formed-in the upper-surface 'of-the block I58 of such depth-as to receive the collar in looking into the mirror 68 adjusts the position of the-X-ray tube by longitudinal movement about the= pivot-54 until he observes in the device"! thecenter or some other given point on the'cas'" setteand sight to be superposed at thereference mark on the mirror, This takescare of the'longitudinal adjustment of the X-raytube. He then adjusts'theX-raytube about the axis "ofthe pins A fill-until he observesinthedevice 20, the center of the cassette and sight to be superposed at the 1 reference mark-in the mirror. This takes'care oflthe transverse adjustmentof the X-ray'tube. Then he goes backto-the device I8 (of Fig. "6'or Fig. 11) and adjusts the 'position'of themirror and sight until the image of the center of the' cassette and sight are observed to register bothtransversely and-longitudinally with the 'r'efer- In using the device shown in'Figs. 13 to 16, in-

elusive, the support I36 is placed over theend of the. shield-i2 and the X-ray tube is th'en' adjusted in both transverse'and longitudinal directionsto bring the center'of' the cassette and" sight at the center of themirr'or as indicated by the cross-reference marks '10. J

When the device shown'in Figs; 17' to 20is employed it is placed withits spindle I against thewallaof the shield and'with the edge I59 in enga'gement withtherolled over 'edgeof the I shield. The operator then looks into the mirror and brings a given point'onthe cassette in line withthe sight and reference mark which therebybrings that portion of the cassette within the I co'ri 'o f-the -projected raysfrom' the X'-ray tube. I

When the line of sight has been established by anyof the meansdescribed, the patient may then be=placed on the table andmoved about until the par-t' that-is"to-be-"'photographed lies 'along the line of'sightwheieupon that part of the patient will be in the correct position to be photographed.

Theinvention described herein may be manufactured and used'by or for the Government ofthe United States'of' America for governmental purposes without the payment of any royalties thereon-or-therefor.

Having fully'described my invention, I claim:

1."In anX-ray'machine. in which the X-ray tube is adjustable about transverse andlongitudinal'axes Withrespect to a cassette, means to facilitate alingment of the X-ray tube transversely and longitudinally of the cassette with respect to a givenpoint thereon, said means comprising a mirror mounted for rotation about-the transverse I axis of-rotation of the X-ray tube, said mirror having a reference mark parallel to the transverse reception of aspring presseddetent I68 for locking the collar in a given position. In order thatthe'collar may" be disposed of without removing itfrom the spindle lfill'in instances where the device'is'to" be used With'a cone shaped shield are'cess' I22' is an out of axis of rotation, a mirror mounted for rotation about the longitudinal axis of rotation of the X- ray tube, said second mirror having a reference mark thereon parallel to said longitudinal axis of rotation, sights cooperating with said mirrors in such a manner that when the images of the said given point on the cassette and sights are observed to be superposed on the reference marks the X-ray tube will be aligned both transversely and longitudinally with respect to said given point and means for adjusting the angular position of one of the mirrors with respect to the X-ray tube so that at a given distance the image of said point on the cassette will be seen to be superposed with its sight both transversely and longitudinally in said one mirror.

2. In an X-ray machine in which the X-ray tube is adjustable about transverse and longitudinal axes with respect to a cassette, means to facilitate alignment of the X-ray tube transversely and longitudinally of the cassette with respect to a given point thereon, said means comprising a mirror mounted for rotation about the transverse axis of rotation of the X-ray tube, said mirror having a reference mark parallel to the transverse axis of rotation, a mirror mounted for rotation about the longitudinal axis of rotation of the X- ray tube, said'second mirror having a reference mark thereon parallel to said longitudinal axis of rotation, sights cooperating with said mirrors in such a manner that when the images of the said given point on the cassette and sights are observed to be superposed at the reference marks the X-ray tube will be aligned both transversely and longitudinally with respect to said given point, and a bracket for pivotally supporting one of said mirrors with respect to the X-ray tube and means for tilting said bracket to cause an image of said point on the cassette andsight to be superposed at the reference mark in both longitudinal and transverse directions in said one mirror.

3. In an X-ray machine in which the X-ray tube is adjustable about transverse and longitudinal axes with respect to a cassette, means to facilitate alignment of the X-ray tube transversely and longitudinally of the cassette with respect to a given point thereon, said means comprising a mirror mounted for rotation about the transverse axis of rotation of the X-ray tube, said mirror having a reference mark parallel to the tranverse axis of rotation, a mirror mounted for rotation about the longitudinal axis of rotation of the X- ray tube, said second mirror having a reference mark thereon parallel to said longitudinal axis of rotation, sights cooperating with said mirrors in such a manner that when the images of the said given point on the cassette and sights are observed to be superposed at the reference mark the X-ray tube will be aligned both transversely and longitudinally with respect to said given point, a bracket for tiltably supporting one of said mirrors with respect to the X-ray tube and a cam for tilting the bracket to cause the image of said point on the cassette and sight to be superposed at the reference mark in both transverse and longitudinal directions on said mirror.

4. In an X-ray machine in which the X-ray tube is adjustable about transverse and longitudinal axes with respect to a cassette, means to facilitate alignment of the X-ray tube transversely and longitudinally of the cassette with respect to a given point thereon, said means comprising a mirror mounted for rotation about the transverse axis of rotation of the X-ray tube, said mirror having a reference mark parallel to the transverse axis of rotation, a mirror mounted for rotation about the longitudinal axis of rotation of the X-ray tube, said second mirror having a reference mark thereon parallel to said longitudinal axis of rotation, sights cooperating with said mirrors in such a manner that when the images of the said given point on the cassette and sights are observed to be superposed at the reference marks the X-ray tube will be aligned both transversely and longitudinally with respect to said given point, and a bracket for tiltably supporting one of the mirrors with respect to the X-ray tube, a cam for tilting the bracket to cause the image on said point on the cassette and sight to be superposed at the reference mark on both transverse and longitudinal directions in said mirror, and means for adjusting the position of the sight with respect to the mirror.

THOMAS RICHARD HAWKS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Haupt Nov. 28, 1939 

